加茂湖(佐渡島)の動物相-予報

抄録

In order to elucidate the faunal characteristics of a brackish lake, Kamo-ko, located in Sado Island in the Japan Sea, a biological survey was carried out during these several years. This lake, 4.86km2 in area, 17.2km in circumference, and 8.7m in the greatest depth, is famous and active for oyster cultivation, and its mouth communicates with Port Ryotsu, i. e., Ryotsu Bay, by a narrow channel, 200m long and 28m wide. Physico-chemical analyses and limnological observations including paleo-liinnological investigations using 18 m core-sample of the bottom were undertaken to know the environmental conditions of the lake. In all ca. 160 species of animals including ca. 50 species of teleost fishes collected up to the present were listed in this paper. All animals, except one leptostracan Crustacea (Nebalia bipes), were of common occurrence in the coasts of Sado Island, however. It is the first characteristic of the faunal elements of Lake Kamo-ko that the tunicates (Ciona intestinalis, Ascidia zara and Botrylloides violaccus), sponge (Ilaliclona permollis) and bivalve mollusk (Mytilus edulis) are dominant species attached to the bamboo-made rafts and the strings suspended from the rafts for oyster cultivation. The bryozoans (JB-ugula neritina and Caulibugula clliata) are also abundant in this lake. The bottom consisting of sand and sandy mud is very narrow and is confined to the marginal zone of the lake. The eel grass (Zostera marina and Z. nana) and other rooted plants flourish in this zone. Most of the bottom covered deeply with a sedimentation of the black mud is devoid of oxygen, seaweeds and benthic fishes. But, even in this worse environment, there are found some polychaetous annelids (Lumbrincris brevicirra, Cirriformia tentaculata and Capitella capitatci) and bivalve mollusk (Musculus senhousia and Modiolus agripetus) which are able to tolerate water pollution. The paucity of organism on the bottom is the second characteristic of the fauna of this lake. The third point is exhibited by the rapid propagation of the recently immigrated barnacles (Balanus eburneus and B. improvisus) insted of other foreign barnacles (73. amphitrite and B. albicostatus). To obtain much more information, further investigations are now in going progress.